1. Field of the Invention
This invention relates to a gas-regulating unit for regulating a gas pressure in a gas-tight liquid-storage tank, in which stored liquid is sealed by covering a top surface of the stored liquid with an isolating-gas, in particular, a gas-regulating unit having a simplified gas piping structure and high serviceability.
2. Description of the Related Art
Conventionally, in a large liquid-storage tank, an internal gas pressure is changed, for example, by a gas space increased or decreased by receiving or releasing stored liquid, or for another example, by the air or vapor increased or decreased by an outside atmosphere condition. For coping with the changing internal gas pressure, a breathing valve system is mounted on the large liquid-storage tank.
On the other hand, when the storage liquid is such as petroleum derivative products or chemical liquids, a gas-tight liquid-storage tank is used for purposes of flame protection and deterioration protection of the storage liquid.
As shown in FIG. 10, when mounting both a breathing valve system 103 and an isolating-gas regulator 104 on the liquid-storage tank 101, they are separately mounted on a roof 102 of the liquid-storage tank 101. FIG. 10 shows an upstream pipe 105 of the isolating-gas, a downstream pipe 106 coupling the isolating-gas regulator 104 to the liquid-storage tank 101, and a control pipe (pressure-sensitive pipe) 107 connecting the liquid-storage tank 101 to the isolating-gas regulator 104.
In the gas-tight liquid-storage tank 101, an internal gas pressure should be slightly higher than an outside atmosphere pressure and kept constant. Therefore, it is necessary to control the isolating-gas supply so precisely as to supply the isolating-gas when the internal gas pressure in the liquid-storage tank 101 is less than a specified level. In the past, we suggested a high-precision isolating-gas regulator for the liquid-storage tank described above in a patent document (Utility Model Document No. JP, H04-13513, Y), and excellent results are obtained.
As shown in FIG. 10 of the present application, and FIG. 1 of the patent document, for mounting the breathing valve system 103 and the isolating-gas regulator 104 on the liquid-storage tank 101, fitting holes 107a, 106aof the control pipe 107 and the downstream pipe 106 should be drilled through a roof 102 of the liquid-storage tank 101. Therefore, a piping-work costs a great deal of money, and a large piping space is occupied for mounting the breathing valve system 103 and the isolating-gas regulator 104 on the liquid-storage tank 101.
Further, when mounting on an existing liquid-storage tank, the fitting holes 107a, 106a of the control pipe 107 and the downstream pipe 106 are newly drilled under limitations. Therefore, the existing liquid-storage tank may be heavily modified. Resultingly, there is a problem that mounting the downstream pipe 106 and the control pipe 107 on the existing liquid-storage tank costs a great deal of money.
Accordingly, an object of the present invention is to provide a gas-regulating unit for regulating an internal gas pressure of a gas-tight liquid-storage tank having no disadvantages of the conventional gas-regulating unit described above, and allowing an isolating-gas regulator to be much easily mounted on the liquid-storage tank, to considerably reduce a mounting cost, and to be mounted on an existing liquid-storage tank without a heavy modification work on a roof of the existing liquid-storage tank.